Device for and method of generating ozone

ABSTRACT

The present invention can provide an electrode member having a substrate member and a coating member. The substrate member can be made of a material selected from the group consisting of titanium, gold coated titanium and other inert conducting materials. The coating member can have a tin dioxide modified by antimony. The electrode member of the present invention can be used for direct generation of ozone in water or through water into a gaseous state.

RELATED PATENT APPLICATION

This patent application claims the benefit of U.S. ProvisionalApplication No. 60/447,948 filed Nov. 10, 2003.

FIELD OF THE INVENTION

The present invention relates generally to the generation of ozone. Inparticular, the present invention relates to an electrode material forgenerating ozone and a method of making the electrode material. Thepresent invention also relates to a high concentration of dissolvedozone and an ozone generation system for generating the same.

BACKGROUND OF THE INVENTION

Ozone has many industrial applications, such as destructing organic andinorganic contaminants in wastewater and sludge, householdsdisinfectants, swimming pools and hospitals, bleaching paper, etchingsemiconductor surfaces, decolorizing water, removing odor from clothing,and terminating pests. [See, Bruno Langlais, David A. Reckhow, DeborahR. Brink; Ozone in Water Treatment application and Engineering, LewisPublishers, INC. 1991, and references discussed therein.] Chlorinationis commonly used in similar applications but will leave undesirablechlorinated organic residues. Ozone on the other hand will selfdisappear in time and leaves fewer potentially harmful residues.

There are two main types of technologies to produce ozone. The firsttype of technology involves the corona discharge process, wherein ozoneis formed from oxygen in air by the corona discharge in an intense andhigh frequency alternating electric field [see, U.S. Pat. Nos.5,882,609; 5,939,030; 6,022,456; 6,153,151]. This type of technologygives low ozone concentration (about 2% to oxygen) and can produceharmful nitrogen oxides. The generation of ozone is in the gas phase andto obtain dissolved ozone, the gaseous ozone is brought into contactwith water and the amount of dissolved ozone is limited by the gas phaseozone concentration and the solubility.

The other type of ozone generation technology is an electrochemical andelectrolytic process, wherein water is decomposed to ozone by passing anelectric current through the electrodes immersed in an aqueouselectrolyte. Since ozone is generated directly in water, this processcan provide high concentration of ozone at a high current efficiency.Over 35% current efficiency has been reported at low temperatures of−30.degree. C. to −65.degree. C. [see, P. C. Foller, C. W. Tobias, J.Electrochem. Soc., 129 (1982), 506]. A recent report discussed a 3.0mg/l concentration of dissolved ozone [see, Tatapudi and Fenton, J.Electrochem. Soc., 140 (1993) 3527].

In aqueous solution, ozone is formed by electrolytic decomposition ofwater, represented by following equations:

3H.sub.2O.fwdarw.O.sub.3+6H.sup.++6.sup.e−, E.degree.=1.51 V,  (1)

and

H.sub.2O+O.sub.2.fwdarw.O.sub.3+2H.sup.++2.sup.e−, E.degree.=2.07V.  (2)

The oxygen evolution reaction, a competitive process at a lowerpotential should occur more easily according to the following equation:

2H.sub.2O.fwdarw.O.sub.2+4H.sup.++4.sup.e−, E.degree.=1.23 V.  (3)

Typically, mostly oxygen and very little ozone is generated uponelectrolysis. Some devices aim for co-generation of oxygen and ozone byelectrolysis of water [see U.S. Pat. No. 5,993,618]. Platinum, alpha andbeta-PbO.sub.2, Pd, Au, RuO.sub.2-DSA's, and glassy carbon in differentelectrolytes have been considered and tested for ozone generation. Gold,RuO.sub.2-DSA's, and glassy carbon have been found to have very lowcurrent efficiency (less than 1%). Platinum shows a current efficiencyfrom 6.5% to 35% at very low temperature of about −50.degree. C. Howeverthe current efficiency falls to around 0.5% at room temperature.Obtaining a high current efficiency at a low temperature will requireadditional equipment and energy cost to make existing systems lessefficient and convenient. PbO.sub.2 electrodes can produce ozone at acurrent efficiency of 13% at room temperature [see, U.S. Pat. No.5,407,550]. With potassium fluoride electrolyte, a 16% currentefficiency at 30.degree. C. has been reported [see, Ten-Chin Wen andChia-Chin Chang, J. Electrochemical Society, 140, (1993) 2764]. However,such a process releases toxic Pb ions into electrolyte solution.

U.S. Pat. Nos. 5,972,196; 5,989,407; 6,287,431 B1; 6,365,026 B1; and6,576,096 B1 disclose dissolved ozone generators using integratedelectrochemical cells. Electrodes that improve dissolved ozoneconcentration and current efficiency at room temperature are needed incommercial applications.

Tin dioxide, a non-toxic semiconductor, has been studied forapplications in sensors, batteries and oxygen evolution. Low currentefficiency and instability had been reported when such tin dioxide wasused for electrochemically generating ozone in concentrated sulfuricacid.

SUMMARY OF THE INVENTION

The present invention can provide an electrode member. The electrodemember can comprise a substrate member and a coating member. Thesubstrate member can be made of a material selected from the groupconsisting of titanium, gold coated titanium and other inert conductingmaterials. The coating member can comprise a tin dioxide modified byantimony. The particles of Sn and Sb can be in an atomic ratio fromabout 6:1 to about 10:1. Additionally or alternatively, a predeterminedamount of nickel can be added in the coating member. The coating membercan comprise particles from about 3 nm to about 5 nm in size.

The electrode member of the present invention can be used for directgeneration of ozone in water or through water into a gaseous state. Thewater can contain an electrolyte selected from the group consisting ofHClO.sub.4, H.sub.2SO.sub.4 and H.sub.3PO.sub.4. The electrolyte can bepresent in a concentration from about 0.01 M to about 0.5 M.

The present invention can also provide an ozone generation systemcomprising such an electrode member to generate ozone efficiently. Theozone generation system can comprise a solid polymer electrolyte, suchas Nafion. Alternative, ozone can be generated in pure water, withoutthe need of dissolved ions. The present invention can further provide adissolved ozone with a high concentration.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description of the present invention will be betterunderstood in conjunction with the accompanying drawings as follows:

FIG. 1 is a SEM surface morphology of an antimony doped SnO.sub.2electrode member of the present invention;

FIG. 2 is a graph illustrating the aqueous ozone concentration as afunction of electric charge; and

FIG. 3 is a graph illustrating the instantaneous aqueous ozoneconcentration as a function of scan potential.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary electrode members and ozone generation systems embodying theprinciples of the present invention will now be described in detail.

The present invention can provide an electrode member. The electrodemember can comprise a substrate member and a coating member. In oneexemplary embodiment, the substrate member can be made of a materialselected from the group consisting of titanium, gold coated titanium andother inert conducting materials. For example, the substrate member ismade of titanium. In an exemplary embodiment, the substrate member canbe made of titanium and be spot-welded with a titanium wire. It will beappreciated that other materials of the substrate member are also withinthe scope of the present invention.

The coating member can be made of various materials and in variousforms. In one exemplary embodiment, the coating member can comprise atin dioxide. In an exemplary embodiment, the coating member can comprisean antimony modified tin dioxide film. For example, the coating membercan comprise SnCl.sub.4.quadrature.5H.sub.20 and SbCl.sub.3. In anotherexemplary embodiment, the coating member can comprise a predeterminedamount of nickel. In one exemplary embodiment, the coating member can bein the form of a solution, before being affixed onto the substratemember. It will be appreciated that other materials and forms of thecoating member are also within the scope of the present invention.

In another exemplary embodiment, the coating member can compriseparticles of various sizes. For example, the coating member can compriseconnected particles of less than 5 nm in size. In one exemplaryembodiment, the connected particles can be from about 3 nm to about 5 nmin size. It will be appreciated that other sizes of the particles arealso within the scope of the present invention.

In a further exemplary embodiment, the coating member can compriseparticles of various ratios. In an exemplary embodiment, the particlesof oxides of Sn and Sb can have an atomic ratio of more than 6:1. Inanother exemplary embodiment, the particles of oxides of Sn and Sbparticles can have an atomic ratio of less than 10:1. In a furtherexemplary embodiment, the particles of Sb and Ni can be in an atomicratio of more than 4:1. In a still further exemplary embodiment, theparticles of Sb and Ni can be in an atomic ratio of less than 10:1. Itwill be appreciated that other ratios of the particles are also withinthe scope of the present invention.

In a preferred embodiment, the electrode member can be made of titaniumand coated with antimony doped tin dioxide with surface morphologycomposed of 3 to 5 nm particles connected and covering substantially theentire surface. In another preferred embodiment, the particles compriseSn and Sb in a ratio from about 6:1 to about 10:1. In a furtherpreferred embodiment, the atomic ratio of Sn:Sb:Ni can be about 500:8:1.The electrode member can yield high concentration of dissolved ozone atroom temperature with high current efficiency.

The electrode member can be prepared in various manners. In oneexemplary embodiment, a substrate member and a coating member of variousforms can be provided, which can be similar to those described above. Ifdesired, the substrate member can be treated or otherwise prepared byvarious conventional methods. For example, the substrate member can beetch cleaned in an acid solution and then rinsed and dried. It will beappreciated that other methods of treating or preparing the substratemember are also within the scope of the present invention.

The substrate member can be affixed with the coating member in variousmanners. For example, the substrate member can be sprayed with, dippedinto, or otherwise coated with the coating member. In an exemplaryembodiment, the coating member can be sprayed with solution of 2.5 gSnCl.sub.4.quadrature.5H.sub.2O and 0.025 g SbCl.sub.3 in 25 ml ofethanol-HCl mixture. In an exemplary embodiment, the coating member canbe dipped into 25 ml ethanol-HCl mixture solution of 2.75 gSnCl.sub.4.quadrature.5H.sub.20 and 0.025 g SbCl.sub.3. It will beappreciated that other methods of affixing the coating member to thesubstrate member are also within the scope of the present invention.

The coated substrate member can then be heat treated in various manners.In one exemplary embodiment, the coated substrate member can be dried,such as at a temperature of about 100.degree. C. for about ten minutes.In another exemplary embodiment, the coated substrate member can becalcined, such as at a temperature of about 520.degree. C. in air for 5mins. The above coating, drying, and calcining steps can be repeated. Inan exemplary embodiment, these steps can be repeat for 12 times. Inanother exemplary embodiment, these steps can be repeat for 20 times. Itwill be appreciated that other heating methods including heatingtemperatures and/or time periods are also within the scope of thepresent invention.

The present invention can also provide a high concentration ozonematerial. In one exemplary embodiment, approximately 35 mg/l aqueousozone can be provided with over 15% current efficiency. In an exemplaryembodiment, the 15% current efficiency only accounts for the dissolvedozone. In a preferred embodiment, such an aqueous ozone can be generatedin a 6 min constant potential polarization at low electrolyteconcentration at room temperate. In another exemplary embodiment, asignificant amount of gaseous ozone can be generated and distinctlydetected by the normal smell test. The measurement of gaseous ozone canshow a much high current efficiency. The solution with dissolved ozonecan decolorize a dye such as indigo instantly. High overpotential ofoxygen evolution was observed in cyclic voltammetry.

Various systems can be used to generate a high concentration ozonematerial. In one exemplary embodiment of the present invention, an ozonegeneration system can be in the form of an electrochemical system forgenerating the high concentration ozone material. In an exemplaryembodiment, the electrochemical system can comprise a cell member forcontaining an electrolyte material of various forms. For example, theelectrolyte material can comprise SnCl.sub.4.quadrature.5H.sub.20 andSbCl.sub.3 in an ethanol-HCl mixture. In another exemplary embodiment,ozone can be generated in pure water, without the need of dissolvedions. It will be appreciated that various other types of ozonegeneration systems are also within the scope of the present invention.

In one exemplary embodiment, the ozone generation system can adopt theelectrode member of the present invention for generating the highconcentration ozone. In an exemplary embodiment, the electrode membercan be used as a working electrode. For example, the electrode membercan be used as an anode member in a electrochemical system. In anotherexemplary embodiment, the electrode member can be positioned on thebottom of the cell member. In a further exemplary embodiment, a constantpotential can be applied to the electrode member, such as at roomtemperature. The constant potential can range from 1.5V to 3V withrespect to a reference electrode. In an exemplary embodiment, theconstant potential can be about 2.5V. It will be appreciated thatvarious other forms of the ozone generation system are also within thescope of the present invention.

The present invention will now be describe in further detail inconnection with the various Examples below.

Example 1

A 0.8.times.0.8.times.0.05 cm.sup.3 titanium (Ti) sheet memberspot-welded with a 1 mm dia. titanium wire was first etch cleaned in a10% boiled oxalic acid solution for 1 hour, then rinsed with distilledwater and dried. An antimony doped SnO.sub.2 electrode member wasprepared by a spray pyrolysis technique on the pretreated Ti substratemember. The spray solution was 2.5 g SnCl.sub.4.quadrature.5H.sub.20 and0.025 g SbCl.sub.3 in 25 ml of ethanol-HCl mixture. After drying thesprayed substrate member at 100.degree. C. for 10 min, the substratemember was calcined at 520.degree. C. in air for about 5 min. Thistreatment was repeated 12 times. The resulting electrode member showed acompact smooth surface morphology with connected particles having adiameter of about 3 to 5 nm (see FIG. 1). The atomic ratio of Sn to Sbin the film is about 7:1 by ICP analysis.

Ozone was generated in a cell with 3 ml 0.1 M HClO.sub.4. The prepareddoped SnO.sub.2 electrode member was used as a working electrode memberpositioned on the bottom of the cell. A 0.8 cm.sup.2 platinum sheet wasused as a counter electrode member positioned at the up-region of theelectrolyte. An Ag/AgCl member was used as a reference electrode memberand positioned closer to the working electrode member. A constantpotential (vs. the Ag/AgCl member) of 2.5V was applied to the workingelectrode member at room temperature. About 35 g/l of ozone dissolved inthe electrolyte was generated in about 6 min. (see FIG. 2). The ozoneconcentration was determined by UV absorption as well as a standardindigo method.

Example 2

An antimony doped SnO.sub.2 electrode was prepared by dipping a Tisubstrate with the same area as described in Example 1 into 25 mlethanol-HCl mixture solution of 2.75 g SnCl.sub.4.quadrature.5H.sub.2Oand 0.025 g SbCl.sub.3. Before drying the dipped the Ti substrate at100.degree. C., excess solution on the substrate surface was removed toleave a thin uniform liquid layer on the substrate surface. Thesubstrate member was calcined at about 520.degree. C. The time periodsfor drying and calcining were the same as in Example 1. The aboveprocess was repeated 30 times. The surface morphology of the resultingelectrode was similar to that shown in FIG. 1. The ratio of Sn to Sb inthe film is about 10:1 by ICP analysis.

Ozone was generated using the same system as in Example 1. SnO.sub.2electrode was performed by cyclic voltammetry in a potential rangingfrom 1.5 V to 3 V (vs. the Ag/AgCl member) at the scan rate of 1 mV/s atroom temperature. FIG. 3 shows the ozone generated against scanpotential.

Example 3

A solution of 1 molar SnCl.sub.4.quadrature.5H.sub.2O, 0.016 molarSbCl.sub.3, and 0.002 molar NiCl.sub.2.quadrature.6H2O in absoluteethanol was used as the coating solution. A titanium sheet can be coatedin the same manner by dip coating and pyrolysis, as described inExample 1. The coating and pyrolysis was repeated 7 times. The resultingNi—Sb doped SnO.sub.2 coated electrode member was tested to give betterozone generation. The current efficiency can reached more than 25% atroom temperature using 0.1 molar perchloric acid electrolyte and withapplied electric potential of 2.2 V (vs. the Ag/AgCl member). The ozonegeneration and measurement was the same as described in Example 1.

It will be appreciated that the various features described herein may beused singly or in any combination thereof. Therefore, the presentinvention is not limited to only the embodiments specifically describedherein. While the foregoing description and drawings represent apreferred embodiment of the present invention, it will be understoodthat various additions, modifications, and substitutions may be madetherein without departing from the spirit of the present invention. Inparticular, it will be clear to those skilled in the art that thepresent invention may be embodied in other specific forms, structures,arrangements, proportions, and with other elements, materials, andcomponents, without departing from the spirit or essentialcharacteristics thereof. One skilled in the art will appreciate that theinvention may be used with many modifications of structure, arrangement,proportions, materials, and components and otherwise, used in thepractice of the invention, which are particularly adapted to specificenvironments and operative requirements without departing from theprinciples of the present invention. The presently disclosed embodimentsare therefore to be considered in all respects as illustrative and notrestrictive.

1-10. (canceled)
 11. A method of improving the current efficiency of anelectrochemical ozone generation system by selective formation of anelectrode member that is to be used in the system, comprising: providinga substrate for an electrode member; forming a layer on the substratethat includes antimony modified tin dioxide; and adding nickel to thelayer, either when the layer is formed, or subsequent to the layerformation step, to improve a current efficiency of an electrochemicalozone generation system that will use the electrode member.
 12. Themethod of claim 11, wherein the forming step comprises: preparing asolution that includes antimony modified tin dioxide; and applying theantimony modified tin dioxide solution to the substrate to form thelayer on the substrate.
 13. The method of claim 12, wherein the addingstep comprises adding nickel to the solution.
 14. The method of claim13, wherein the adding step comprises adding nickel to the solution inan amount that causes the resulting electrode member to provide acatalytic effect that increases a current efficiency of anelectrochemical ozone generation system that employs the electrodemember.
 15. The method of claim 12, wherein the adding step comprisesapplying nickel to the layer after it has been formed on the substrate.16. The method of claim 12, wherein the applying step comprises:spraying the antimony modified tin dioxide solution onto the substrate;drying the solution; and calcining the resulting electrode member. 17.The method of claim 16, further comprising repeating the spraying,drying and calcining steps a predetermined number of times.
 18. Themethod of claim 17, wherein repeating the spraying, drying and calciningsteps a predetermined number of times comprises repeating the spraying,drying and calcining steps between 12 and 30 times.
 19. The method ofclaim 16, wherein drying the solution comprises heating the electrodemember at about 100° C. for about 10 minutes.
 20. The method of claim16, wherein calcining the electrode member comprises calcining theelectrode member at a temperature of about 520° C. in air for about 5minutes.
 21. The method of claim 12, wherein the applying stepcomprises: dipping the substrate into the antimony modified tin dioxidesolution; drying the solution; and calcining the resulting electrodemember.
 22. The method of claim 21, further comprising repeating thedipping, drying and calcining steps a predetermined number of times. 23.The method of claim 22, wherein repeating the dipping, drying andcalcining steps a predetermined number of times comprises repeating thedipping, drying and calcining steps between 12 and 30 times.
 24. Themethod of claim 21, wherein drying the solution comprises heating theelectrode member at about 100° C. for about 10 minutes.
 25. The methodof claim 21, wherein calcining the electrode member comprises calciningthe electrode member at a temperature of about 520° C. in air for about5 minutes.
 26. The method of claim 11, wherein providing the substratefor the electrode member comprises providing a substrate membercomprising an inert conductive material.
 27. The method of claim 11,wherein the forming and adding steps are conducted so as to result in asurface morphology of approximately 3 to 5 nm connected particlescovering substantially all of the substrate.
 28. A method of improvingthe current efficiency of an electrochemical ozone generation systemthat uses an electrode member, comprising: providing an electrode memberfor an electrochemical ozone generation system, the electrode memberincluding antimony modified tin dioxide; and adding an amount of nickelto the antimony modified tin dioxide electrode member such that thenickel provides a catalytic effect that improves a current efficiency ofan electrochemical ozone generation system employing the electrodemember, as compared to an electrochemical ozone generation system havingan electrode that lacks nickel.
 29. The method of claim 28, wherein theadding step is conducted such that the nickel added to the antimonymodified tin dioxide electrode member increases the percentage ofcurrent applied to the electrode that results in the generation ofozone.
 30. The method of claim 28, wherein the adding step is conductedsuch that the nickel added to the antimony modified tin dioxideelectrode member decreases the percentage of current applied to theelectrode that results in the generation of oxygen.